RU2729570C2 - Flexible laminar material for printed retort-packages - Google Patents

Abstract

FIELD: materials for food products packing.

SUBSTANCE: invention relates to flexible laminar material for printed retort-packages. Proposed package comprises flexible multilayer substrate with reversible printing layer. Note here that said reversible printing layer comprises one or several layers of cross-linked ink. Invention describes a method of making such a multilayer laminar material.

EFFECT: invention provides printing flexible retort-packages, which can withstand critical humidity, pressure and temperature without fading, image distortion and/or deterioration of printing sharpness.

18 cl, 1 tbl, 4 ex

Description

AREA OF TECHNOLOGY

The present invention relates to a flexible printable multilayer substrate for retort packaging and to a method for making such a substrate.

LEVEL OF TECHNOLOGY

Packaged foods often need to be sterilized. One way to sterilize packaged food is autoclaving, which is the treatment of packaged food with heat and pressure.

Instead of being packaged in cans and glass containers, food is increasingly being packaged in flexible retorts. Packaging material for flexible retorts usually contains a middle hydro and gas barrier layer, which is usually a metal foil, metallized film or transparent protective film, a polymer outer layer glued to one side of the middle gas barrier layer and forming the outer surface of the package , and a heat-sealable inner layer of polymer film adhered to the other side of the middle gas barrier layer and forming the inner surface of the package. The packaging material can also contain an additional layer of polymer film. The outer polymer film layer is usually polyester and the inner polymer film layer is usually non-oriented polypropylene. The additional plastic film layer can be nylon or other similar material.

Each of the layers can withstand the autoclaving process without melting or substantially decomposing. In general, autoclaving consists of heating the packaging container to a temperature of 100 to 135 ° C, at an elevated pressure of 0.5 to 1.1 bar, for a period of 20 to 100 minutes.

Laminates for retort packs are disclosed, for example, in US 4310578 A, US 4311742 A, US 4308084 A, US 4309466 A, US 4402172 A, US 4903841 A, US 5273797 A, US 5731090 A, EP 1466725 A1, JPH 09267868 A , JP 2002096864 A and JP 2015066 721 A.

If alphanumeric characters and / or images are to be printed on the packaging, the outer layer of the laminate can be reverse-printed before being laminated to an additional layer. Alternatively, the outwardly facing surface of the laminate can be printed and then autoclaved with varnish.

JPH 02117826 A discloses a packaging material comprising a printed layer composed of polyethylene terephthalate with a protective layer of polycarbonate, polypropylene or fluoroplastic on the outer surface and with aluminum foil and polypropylene film on the inner surface of the printed film layer.

From EP 1232855 A2, a laminate is known comprising an outer layer of polyethylene terephthalate, a second nylon layer and an inner polypropylene layer. To bond the layers, a solvent-free adhesive was used that includes surface-modified laminated montmorillonite clay plates. The polyethylene terephthalate layer can be printed in reverse using special ink systems.

EP 2 100 729 A1 describes a laminate comprising a biaxially oriented plastic layer as an outer layer and a weldable layer as an inner layer, as well as optionally at least one middle layer, the outer layer being frontally printed, with the ink print being coated with a thermal protective layer. varnish.

EP 1541340 A1 discloses a laminate comprising a first multilayer structure having a reversible or embossed carrier layer and a gas barrier layer, and a second multilayer structure comprising a sealing layer, at least one anti-movement layer, at least one barrier layer and white or lightly colored layer.

In the field of printing and decorating laminates, the most common liquid ink printing methods are based on drying or curing individual ink layers by evaporation of water or volatile organic compounds. These processes are energy intensive and often have a negative impact on the environment due to the release of solvent or greenhouse gases into the atmosphere. US 2011/0027543 A1 discloses a polyurethane resin especially suitable for use in printing inks for the manufacture of laminated packaging. The polyurethane resin maintains the bond strength of the laminate before and after the laminate printed with an ink containing the polyurethane resin is sterilized.

The introduction of radiation curable inks, such as ultraviolet (UV) and electron beam (EB) curable inks, can reduce solvent emissions and significantly improve printing productivity.

There are two main technologies used in radiation-curable inks. The first uses free radical components to initiate the polymerization of reactive functional groups, in particular, with ethylene double bonds. The most commonly used reactive groups are (meth) acrylate and in particular acrylate groups, disclosed, for example, in WO 97/31071 A1, US 2015/0116432 A1 and US 2015/0184005 A1.

Another technology used in radiation curing is the creation of very strong acids to initiate cationic polymerization of reactive functional groups such as cyclic esters, for example oxirane or oxetane, preferably alicyclic epoxies, allyl esters and vinyl esters, disclosed, for example, in US Pat. No. 5,674,922. A and US 20100136300 A1.

The use of radiation curable ink in printed flexible packaging is disclosed, for example, in US 2008/021570 A1, EP 2133210 A1, EP 2720877 A1, EP 0741644 A1, EP 2305758 A1, US 2002/119295 A1, EP 1159142 A1, US 2013/0233189 A1 and US 2005/019533 A1.

WO 2002/022462 A1 discloses an autoclaved laminate comprising an inner layer and a first plastic layer selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and mixtures thereof, said plastic layer having printing ink, the printing being protected by a transparent varnish layer curable by ultraviolet radiation and electron beam. The inks for printing are selected from the group consisting of radiation curable inks, acrylate based inks, polyvinyl butyral based inks, and water based inks.

WO 2008/094085 A1 discloses an autoclaved laminate containing decorative printing obtained by means of a UV-curable printing ink and completely or partially coated with an outer layer of a UV-curable varnish.

Typical disadvantages and / or limitations of radiation curable inks are the presence of residual low molecular weight compounds and the fragility of the ink layer.

In addition to the standard printing technologies used in flexible packaging, such as, for example, solar gravure and flexographic printing, new technologies that have emerged over the past ten years have gained some success.

Among these technologies, the most notable is digital printing, such as inkjet printing and liquid electrography.

Digital printers and methods are known in the field of printing and are generally described in, for example, US 2002/154928 A1, US 6529288 B1, US 2002/073857 A1, WO 97/37286 A1, US 5819667 and US 5777576 A.

Electrographic printing on plastic, paper or metal is known, for example, from US 2011/0256478.

JP 2015027774 A discloses an autoclaved digitally printed laminate containing reverse printed oriented nylon laminated with an ester based adhesive, with its non-printed side onto transparent polyethylene terephthalate and its printed side onto non-oriented polypropylene.

It has often been noted that digital printing on flexible packaging containers is adversely affected during autoclaving, deteriorates dramatically and even completely loses its characteristic print quality. In addition, in the particular case where the laminate contains a reverse printed layer, delamination defects often appear at the interface of the printed polymer layer.

Without considering the advantages inherent in prior art systems, however, it is clear that there is still a need to provide printable flexible retorts that can withstand critical humidity, pressure and temperature without fading, image distortion and / or degradation. sharpness of the print.

The task of the invention

The present invention is directed to a retort package comprising a flexible multilayer substrate that contains one or more seals, preferably digital stamps, and a method for manufacturing said multilayer substrate, said substrate having particular advantages over the prior art solutions mentioned above.

DISCLOSURE OF THE INVENTION

The present invention discloses a retort package comprising a flexible multilayer substrate, said substrate comprising a reverse-printed layer, said reverse-printed layer comprising one or more layers of ink, characterized in that the concentration of ethylenically unsaturated groups or alicyclic epoxides is less than 0.05 meq / g, preferably less than 0.03 meq / g, more preferably less than 0.01 meq / g, most preferably less than 0.005 meq / g.

Preferred embodiments of the present invention comprise one or more of the following features:

- the reverse-printed layer contains a primer layer sandwiched between the cross-linked ink layers and the substrate,

- the layer with reverse printing is characterized in that the total thickness of the primer layer and the ink layer (s) is from 0.4 to 4 μm, preferably from 0.6 to 3.5 μm, more preferably from 0.8 to 3 μm,

- the layer with reverse printing is characterized in that the thickness of the primer is from 0.01 to 0.5 μm, preferably from 0.05 to 0.4 μm, more preferably from 0.1 to 0.3 μm,

- the retort package contains an external structure, and the specified external structure contains one or more layers with a reversible print, and the lower surface of the external structure is in contact with the upper surface of the middle structure, and the specified middle structure contains one or more barrier layers, and the lower surface of the middle the structure is in contact with the upper surface of the inner structure, and the specified inner structure contains a sealing layer,

the cross-linked ink layer of the flexible laminate remains substantially intact after autoclaving at a temperature of at least 100 ° C, preferably at least 120 ° C.

The present invention also relates to a method for making a flexible multilayer substrate to be used in retort packaging, comprising the steps of:

a) provide a flexible backing,

b) applying at least one digital print with at least one ink composition by a digital printing process, said ink composition substantially free of meth (acrylic) double bonds and / or cycloaliphatic epoxy groups,

c) subjecting the digital print to electron beam irradiation to form a crosslinked digital print,

d) providing contact and bonding of the flexible substrate containing cross-linked digital printing on its printed side with an additional layer to form at least a portion of the multilayer substrate.

Preferred embodiments of a method for manufacturing a printed flexible substrate comprise one or more of the following features:

- at least one ink composition is essentially free of components containing molecular structures with free and / or end-to-end ethylenically unsaturated double bonds, and components containing alicyclic epoxides,

- the flexible packaging substrate in step a) is plasma treated, preferably corona plasma treated,

- an additional step in which the primer formulation is applied before starting step b),

- the digital printing process in step b) is liquid electrographic printing,

- the dose of irradiation by the electron beam in step c) is at least 15 kGy, preferably at least 20 kGy, more preferably at least 25 kGy,

- the dose of the electron beam irradiation in step c) is from 20 to 100 kGy, preferably from 25 to 80 kGy, more preferably from 30 to 60 kGy,

- irradiation with an electron beam in step c) is carried out at an oxygen concentration of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, most preferably less than 150 ppm,

- in step a), the flexible substrate contains polyethylene terephthalate, high-density polyethylene, oriented polypropylene, oriented polyamide or polystyrene,

- the primer composition contains one or more polyacrylamides,

- the ink formulation contains one or more (meth) acrylic (co) polymer resins,

- ink formulation contains:

- from 20 to 95% by weight of the hydrocarbon liquid carrier,

- from 5 to 80% by weight of one or more (meth) acrylic (co) polymer resins,

- from 10 to 50% by weight of one or more carboxylated ethylenes containing copolymer co-resins and

- from 0.1 to 80% by weight of one or more dyes.

CARRYING OUT THE INVENTION

The present invention discloses a retort package comprising a flexible backing, said flexible backing having a middle structure comprising a barrier layer, an outer structure comprising a reverse-printed polymer layer laminated to one side of the middle structure, and an inner structure comprising a seal layer laminated to the opposite side of the middle structure, the substrate being adapted to withstand the autoclaving process at a temperature of more than 100 ° C, preferably more than 120 ° C without substantially degrading the print quality, wherein the print is obtained by printing, preferably digital printing, with standard inks, which are then cross-stitched by irradiation with an electron beam.

Upon autoclaving, the cross-linked ink layers remain substantially intact. In the present invention, the expression “substantially intact” means that the print sharpness does not drop and / or its constituent colors do not fade.

In the present invention, the expression “print sharpness” means that the outline and resolution of drawings and images, as well as the clarity of letters, numbers and symbols, do not change up to 1 mm. The sharpness of the image is assessed with the naked eye.

By fading in the present invention is meant that color fastness, measured as ΔE according to the international standard CIELab, is less than 4, preferably less than 3, more preferably less than 2.

After autoclaving, the bond strength between the reverse-printed resin layer and the layer in contact with the reverse-printed layer on its printed side, measured in accordance with ASTM F904-1998 (reapproved 2008), is at least 1.0 N / 15 mm, preferably 1.3 N / 15 mm, more preferably at least 1.5 N / 15 mm, and at least 10%, preferably at least 20%, more preferably 30%, most preferably at least 40% or even at least 50% higher than the bond strength in the case of digital printing not exposed to electron beam irradiation.

Both the inner and outer structures can contain one or more barrier layers.

The middle structure may contain one or more layers that do not have significant barrier properties.

The barrier layer used in the flexible substrate according to the present invention provides impermeability to gases as well as odors and, in particular, prevents oxygen from entering the contents of a package made from said substrates.

The barrier layer can be a metal foil, for example, aluminum foil or a pre-formed laminate comprising aluminum foil and one or more polymer films, or a metallized polymer film such as metallized oriented polypropylene.

The barrier layer may be a coated polymeric film, the coating being selected from the group consisting of alumina, silicon oxide, magnesium oxide, cerium oxide, hafnium oxide, tantalum oxide, titanium oxide, yttrium oxide, zirconium oxide, and mixtures thereof.

Preferably, the barrier layer comprises a ceramic coating of alumina (AlO _x ) or silicon oxide (SiO _x ) on a polyethylene terephthalate film. The ceramic coating can be formed by physical and / or chemical vapor deposition, plasma-assisted chemical vapor deposition, or plasma polymerization.

Other barrier layers include carbon layers, polyacrylates, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, cellophane, polyamide, and polyvinylidene chloride. In this case, it is possible to use a combination of barrier layers.

Preferably, the inner structure comprises a sealing layer, for example, heat sealable polyester, high density polyethylene, polypropylene or rubber modified polypropylene. Preferably, the inner structure comprises blown polypropylene, non-oriented polypropylene, or extrusion coated polypropylene.

The outer structure contains a cross-linked polymer layer with digital reversible printing, and the specified polymer layer is selected from the group consisting of polyester, polyamide, polyolefin, polycarbonate, polystyrene and their copolymers, and the specified digital printing is cross-linked by irradiation with an electron beam.

Preferably, the outer structure comprises a film of oriented polyethylene terephthalate cross-linked by electron beam and digitally reversible, oriented polypropylene, high density polyethylene, oriented polyamide and / or polystyrene.

In one embodiment, the outer structure comprises a digitally reversible printed oriented polyethylene terephthalate layer cross-linked by electron beam and having a ceramic coating, the seal being in contact with the ceramic coating.

Multilayer substrates can be made by laminating by gluing and / or extrusion, or a combination thereof.

In the case of sizing lamination, the different layers are laminated with autoclaved adhesives such as, for example, an organosilane adhesive, an epoxy adhesive or a polyester or polyurethane based adhesive.

Preferably, the adhesive is a two-component adhesive, more preferably a two-component polyurethane-based adhesive containing one or more polyols and one or more polyisocyanates, preferably aliphatic polyisocyanates.

In the case of extrusion lamination, it is possible to use adhesive layers containing modified polypropylene, such as silane-grafted polypropylene or polypropylene grafted with maleic anhydride, polyesters, ethylene copolymers, polyurethanes or polyacrylates.

At least one layer of the outer structure is reversible by digital printing, preferably liquid electrography.

By the expression "reversibly" is meant that ink is applied to the surface of a transparent layer, said surface subsequently being contacted and laminated to another layer, the ink being visible through the layer due to its transparency.

The printed retort substrates according to the present invention preferably comprise:

an external structure containing:

- cross-linked film made of oriented polyethylene terephthalate with digital reverse printing, thickness from 5 to 80 microns, glued to

medium structure containing:

- a film of oriented polyethylene terephthalate with a ceramic coating, thickness from 5 to 50 microns and / or

- an oriented polyamide film with a thickness of 5 to 40 microns,

and / or

- an ethylene-vinyl alcohol copolymer film with a layer thickness of 3 to 10 microns, glued to

internal structure containing

- film made of non-oriented polypropylene with a thickness of 40 to 120 microns,

wherein the outwardly facing surface of the substrate is polyethylene terephthalate and the inwardly facing surface of the substrate is non-oriented polypropylene,

moreover, the inner and outer structures optionally contain one or more barrier layers, while the middle structure optionally contains one or more layers that do not have significant barrier properties,

wherein the structures / layers are glued with an adhesive or an adhesive layer,

wherein the reverse-printed oriented polyethylene terephthalate film is obtained by curing the liquid electrographic printing by means of an electron beam.

The present inventors have found that digital prints obtained by printing with standard formulation inks containing (meth) acrylic copolymer resins are autoclavable due to electron beam irradiation.

In the present invention, by “standard ink formulations” is meant ink formulations that are not designed for UV or electron beam curing, that is, ink formulations that are substantially free of (meth) acrylic double bonds and / or alicyclic epoxides.

The constituents of the ink used in the present invention are substantially free of free and / or terminated ethylenically unsaturated functional groups such as (meth) acrylic, vinyl, allyl and fumaric acid functional groups.

By "free ethylenically unsaturated groups" in the present invention is meant functional groups that are not included in the molecular backbone, unlike, for example, unsaturated polyesters or butadiene containing (co) polymers, in which ethylenically unsaturated groups are part of the main chain ...

By the expression "substantially free of ethylenically unsaturated groups" in the present invention is meant that the concentration of ethylenically unsaturated groups is less than 0.2 mEq / g, preferably less than 0.1 mEq / g, more preferably less than 0.05 meq / g, most preferably less than 0.01 meq / g.

By the expression "substantially free of alicyclic epoxides" in the present invention is meant that the concentration of alicyclic epoxides is less than 0.2 mEq / g, preferably less than 0.1 mEq / g, more preferably less than 0.05 mEq / d, most preferably less than 0.01 mEq / g.

Preferably, the ink formulations used in the present invention do not have (meth) acrylic double bonds and / or acyclic epoxides.

Preferably, the ink formulations used in the present invention do not have components containing free and / or terminated ethylenically unsaturated functional groups.

Prior art resins specially designed for UV and electron beam curing are generally characterized in that the concentration of ethylenically unsaturated groups or acyclic epoxides is greater than 1.0 meq / g and even greater than 1.5 meq / g. , and a high concentration is necessary to ensure chemical activity.

Despite the substantial absence of such ethylenically unsaturated groups or alicyclic epoxides in the inks used in the present invention, electron beam irradiation crosslinks the polymer chains, with the crosslinks preferably being carbon-carbon crosslinks.

The carbon-carbon cross-links of the electron beam crosslinked ink according to the present invention are preferably characterized in that the carbon atoms are tertiary or quaternary carbon atoms.

More preferably, the carbon-carbon crosslinks are of the type (R ¹ ) ₂ R ² C -C (R ¹ ) ₂ R ³ , where:

- R ¹ is a segment of (meth) acrylic copolymer,

- R ² represents a hydrogen atom or a segment of (meth) acrylic copolymer,

- R ³ represents a hydrogen atom, a methyl group or a (meth) acrylic copolymer segment,

determined according to Fourier transform infrared spectroscopy.

The concentration of residual ethylenically unsaturated groups or acyclic epoxides in cross-linked inks obtained by irradiation of inks intended for cross-linking by means of ultraviolet rays or an electron beam, and having high concentrations of ethylenically unsaturated groups or alicyclic epoxides, exceeds 0.05 meq / g, more preferably exceeds 0.1 mEq / g, most preferably exceeds 0.2 mEq / g, with said residual ethylenically unsaturated groups or acyclic epoxides resulting from incomplete conversion due to an increase in viscosity after an increase in the degree of transverse stitching.

The concentration of ethylenically unsaturated groups or alicyclic epoxides and the degree of conversion can be determined by combining titrations, such as, for example, iodometric titrations, with infrared spectroscopy based on Fourier transform.

Despite the substantial absence of such ethylenically unsaturated groups or alicyclic epoxides in the ink used in the present invention, the electron beam irradiation provides cross-linking of the ink components.

The concentration of ethylenically unsaturated groups or acyclic epoxides in standard ink crosslinked on a substrate according to the present invention is less than 0.05 mEq / g, preferably less than 0.03 mEq / g, more preferably less than 0.01 mg- eq / g, most preferably less than 0.005 meq / g.

Preferably, conventional ink crosslinked on a substrate according to the method of the present invention is free of ethylenically unsaturated groups and alicyclic epoxides.

Preferably, the standard liquid ink formulations to be used in the present invention contain one or more (meth) acrylic (co) polymer resins.

More preferably, the liquid ink comprises a liquid carrier, a resin, preferably a (meth) acrylic (co) polymer resin, a co-resin, and a colorant.

The co-resin preferably comprises a copolymer of ethylene and acrylic acid, a maleic anhydride polymer having polyethylene grafted onto the polymer, and combinations thereof. The amount of the co-resin is 10 to 50% by mass, preferably 10 to 40% by mass, more preferably 10 to 20% by mass of the ink formulation.

The resin preferably contains (co) polymers of (meth) acrylic acid, copolymers of (meth) acrylic acid and alkyl (meth) acrylate, copolymers of ethylene and (meth) acrylic acid, copolymers of ethylene and alkyl (meth) acrylate, copolymers of ethylene, (meth) acrylic acid and alkyl (meth) acrylate, copolymers of ethylene and vinyl acetate, copolymers of ethylene, (meth) acrylic acid and vinyl acetate, copolymers of ethylene, alkyl (meth) acrylate and vinyl acetate, copolymers of ethylene, (meth) acrylic acid, alkyl (meth) acrylate and vinyl acetate, copolymers of (meth) acrylic acid and vinyl acetate, copolymers of alkyl (meth) acrylate and vinyl acetate, copolymers of (meth) acrylic acid, alkyl (meth) acrylate and vinyl acetate, polymers such as, for example, polyethylene, polystyrene, isotactic polypropylene, polyesters, polyvinyl toluene, polyamides, butadiene-styrene copolymers, epoxy resins, low molecular weight ionic polymers of ethylene and acrylic acid, and combinations thereof.

The amount of resin is 5 to 80% by mass, preferably 10 to 60% by mass, more preferably 15 to 40% by mass, based on the total weight of the ink formulation.

The liquid carrier is preferably a hydrocarbon selected from the group consisting of (iso) paraffinic hydrocarbon, aliphatic hydrocarbon, isomerizable aliphatic hydrocarbon, branched chain aliphatic hydrocarbon, aromatic hydrocarbon, dearomatized hydrocarbon, halogenated hydrocarbon, cyclic hydrocarbon, functionalized hydrocarbon, and combinations thereof ... Preferably, the carrier is 3,5,7-trimethyldecane.

The amount of the carrier liquid is 20 to 95% by mass, preferably 40 to 90% by mass, more preferably 60 to 80% by mass of the ink formulation.

Colorants are organic and / or inorganic colorants. Dyes may contain cyan dyes, magenta dyes, yellow dyes, violet dyes, orange dyes, green dyes, black dyes, and combinations thereof. The amount of dye is 0.1 to 80% by weight of the ink formulation.

The ink formulation may further include charge activators such as, for example, aluminum tristearate, and charge carriers, such as, for example, sulfonic acids and their salts. Charge activators are generally used in amounts ranging from 0.1 to 5% by weight, preferably from 0.5 to 4% by weight, more preferably from 1 to 3% by weight of the ink formulation, with charge carriers being in general, used in an amount equal to from 0.001 to 1% by weight of the ink formulation.

The side of the layer to be digitally printed may first undergo physical compatibilization, such as plasma treatment, preferably corona plasma treatment, flame treatment, and the like. to change its surface energy. Another method is to apply a primer to a substrate. Physical surface treatment can also be carried out prior to primer application.

The primer used in the present invention can be applied by digital printing. The primer preferably contains a liquid carrier and a resin, the carrier preferably being a hydrocarbon as described above, the resin being preferably selected from the group consisting of cellulose, dextrin, maltose monohydrate, polyacrylic acid, polyvinyl alcohol, styrene maleic anhydride copolymer, maleimide copolymer, polyacrylamide, sucrose octaacetate, sucrose benzoate, and combinations thereof. Preferably, the primer used in the present invention contains polyacrylamide.

The term "polyacrylamide" includes all (alk) acrylamide homopolymers as well as copolymers and functionalized polyacrylamides. Polyacrylamides can be anionic, cationic and non-ionic. Various monomers, preferably ethylenically unsaturated monomers, can be copolymerized with (alk) acrylamide monomers to form polyacrylamides.

At least one layer of the outer structure of the multilayer substrate according to the present invention has on its reverse side a cross-linked digital printing, preferably obtained by liquid electrographic printing and irradiation with an electron beam.

A flexible substrate according to the present invention has at least one layer containing a primer and one or more ink layers digitally printed on the reverse side of at least one layer, with the total thickness of the primer layer or ink layer (or layers) being from 0.4 to 4 microns, preferably from 0.6 to 3.5 microns, more preferably from 0.8 to 3 microns, while the thickness of the primer layer is 0.2 microns.

In a digital printing press, the layer is loaded into a primer unwinder, where it is corona treated to provide better wetting and ink adhesion. In the next step, a primer is applied to ensure covalent bonding between the substrate and the ink. The primer is dried in a drying unit, after which it passes into a printing apparatus, preferably a liquid electrographic printing apparatus.

Preferably, the biaxially oriented polyethylene terephthalate layer is fed from a feed roll and processed in a plasma processing unit, preferably corona plasma processing; further in the unit for applying a primer and in a printing unit, preferably a digital printing unit, more preferably an electrography unit with liquid ink; and in the electron beam irradiation unit.

Liquid electrography involves creating an image on a photoconductive surface with a laser, applying ink having charged particles to the photoconductive surface so that they are selectively associated with the image, and then transferring the charged particles in the form of an image to a printed resin layer.

The photoconductive surface is usually located on the cylinder and is often referred to as a forming plate (FP). The photoconductive surface is selectively charged by a latent electrostatic image having image and background regions with different potentials. For example, an electrostatic ink composition containing charged particles in a liquid carrier can be contacted selectively with a charged photoconductive surface. Charged particles are linked to image areas in the latent image, while background areas remain clear. Next, the image is transferred to the printed resin layer directly or, more often, first to an intermediate transfer element, which can be a soft swellable web, and then to the printed resin layer. The transfer of ink is enhanced by the application of an electric field, and the liquid ink carrier evaporates from the canvas. The hot melt ink adheres to the resin layer through pressure and tack. The process is repeated for each color. In principle, the ink is transferred to the polymer without altering or saturating the substrate. Thus, the quality of the resulting image is very high.

The digitally printed polymer layer is essentially bombarded with an electron beam.

An electron beam processing device typically contains three zones, that is, a vacuum chamber zone where the particle beam is generated, a particle accelerator zone, and a treatment zone. In a vacuum chamber, the tungsten filament (or filaments) are heated, for example, to a temperature of 2400K, which is the temperature of emission of thermionic electrons of tungsten, to create a cloud of electrons. Further, a positive voltage difference is applied to the vacuum chamber to extract and simultaneously accelerate the electrons. The electrons then pass through the thin foil and enter the treatment area. The thin foil acts as a barrier between the vacuum chamber and the processing area. Accelerated electrons leave the vacuum chamber through a thin foil and enter the processing zone.

The electron energies are in the range from 10 to 300 keV, preferably from 20 to 250 keV, more preferably from 30 to 200 keV.

The radiation dose received by digital ink is in the range of 15 to 100 kGy, preferably 20 to 80 kGy, more preferably 30 to 60 kGy.

Electron beam irradiation of digital printing is carried out in an oxygen-deficient area obtained by applying a vacuum or by using an inert gas blanket such as a nitrogen blanket.

By "oxygen deficient environment" in the present invention is meant an oxygen concentration of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, most preferably less than 150 ppm. or even less than 100 ppm.

After electron beam bombardment of the digitally printed polymer layer, said layer is additionally processed in a multilayer substrate.

In the lamination process, a polymer layer having a cross-linked digital printing is laminated with its printed side onto a middle structure, the middle structure preferably comprising a barrier layer, more preferably a polyethylene terephthalate layer, with a ceramic coating and / or an oriented polyamide layer. The middle structure is laminated with its other side onto the inner structure, the inner structure preferably comprising a non-oriented polypropylene sealing layer and optionally having one or more additional layers, for example a polyethylene alcohol barrier layer.

In one embodiment, a polymer layer containing crosslinked digital printing is glued with the printed side to a laminate containing a middle and inner structure.

The multilayer substrate can be subsequently welded at a temperature of 100 to 250 ° C, preferably 110 to 230 ° C, more preferably 120 to 220 ° C under a pressure of 20 to 120 N / cm ² , preferably 20 to 110 N / cm ² , more preferably 40 to 100 N / cm ² to form a flexible retort package such as a retort bag.

Examples of

The following illustrative examples are given only to illustrate the present invention, not to limit or otherwise determine the scope of its legal protection.

Example 1

A 12μm thick polyethylene terephthalate (PET) film was corona plasma treated (400W) and subsequently introduced into an HP 20000 Indigo digital printing system, where it was coated with Michelman's colorless Digiprime® 050 digital primer at a layer thickness of approximately 0.2 μm, and

- half of the surface of the PET film was coated with a layer of blue ink, with a layer thickness of approximately 1 μm,

- and on the other half, a blue pattern was printed containing 10 vertical lines and 10 horizontal lines, each of which was 50 mm long and 0.3 mm wide, at intervals of 1 mm, 2 mm and 3 mm, respectively, and which intersected at an angle of 90 °, and the thickness of the printed pattern is 1 μm.

Next, the digitally printed PET film was transferred to a vacuum electron beam processing apparatus.

The electron beam gun has a computer controlled deflection system programmed so that the gun emits beams into a drum, which is typically used as a coating drum. The printing film passing over this drum was irradiated with an electron beam gun. The deflection system was programmed to electronically scan a surface of 200 mm (winding direction) by 400 mm (transverse direction) and, accordingly, irradiate this surface. During the passage of the web at a speed of 15 m / min through this zone, the ink was irradiated for 0.6 seconds. The electron beam gun operated with an accelerating voltage of 35 kV, resulting in an electron energy of 35 keV. The emission current was 0.42 A, and the total irradiation power when scanning a given area was 15 kW.

The electron-beam-irradiated digitally printed PET sample was laminated with the printed side with 8 µm aluminum foil, while the aluminum foil was laminated with the opposite side with a 60 µm polypropylene film. Lamination was carried out using a two-component water-based Liofol® UR364 / Liofol® UR6055 polyurethane adhesive (Henkel) at a ratio of 13/1, with a dry layer thickness of 4 μm.

Next, the flexible multi-layer support was sterilized in an autoclave at 121 ° C for 30 minutes.

Example 2

Polyethylene terephthalate 72 microns thick coated with SiO _x, was treated with corona plasma, it was applied colorless primer to digital printing, and it was printed as in Example 1, after which it was glued together with the printed side with a film of biaxially oriented polyamide 15 microns thick and the polyamide film was glued on the opposite side to a white film of non-oriented polypropylene with a thickness of 70 μm. The lamination was carried out using a two-part water-based polyurethane adhesive Adcote ™ 811A / Catalyst 9L10 (Rohm and Haas) in a 92/8 ratio, with a dry layer thickness of 2 μm. Next, the flexible multi-layer support was sterilized in an autoclave as in example 1.

Example 3

The ink quality of the laminate in Examples 1 and 2 was determined for color inks exposed to various doses of electron beam irradiation.

Table 1:

- line 1 indicates the radiation dose, in kGy, applied to the digitally printed image prior to lamination,

- line 2 indicates color fastness / discoloration upon autoclaving, measured as ΔE according to the international standard CIELab, according to DIN6174,

- line 3 denotes the gloss reduction measured at 60 ° according to ASTM D523 after autoclaving, the gloss reduction being G ^init - (100 * G ^ret / G ^init ), where G ^init is the gloss before autoclaving and G ^ret is gloss after autoclaving,

- line 4 denotes the sharpness of the image after autoclaving, with the value presented denotes the smallest picture interval with a clear outline and resolution (the initial sharpness was at an interval of 1 mm),

- line 5 denotes the adhesion strength (N / 15 mm) between the polymer layer with reverse printing and the layer in contact with the specified layer with reverse printing from its printed side, when peeled at an angle of 90 ° at a speed of 100 mm / min in accordance with ASTM standard F904-1998 (reconfirmed in 2008), after autoclaving.

Table 1

Example 1 Example 2 Radiation dose 0 15 20 thirty 0 15 20 thirty Color change 5.5 5.2 3.5 1,2 5.0 4.5 3.8 0.8 Reducing gloss 35 32 18 3 thirty 26 15 1 Image sharpness > 3 > 3 2 1 > 3 > 3 2 1 Bonding strength 1.09 1.03 1.22 1.70 1.05 1.10 1.35 1.90

Example 4

Examples 1 and 2 were repeated, with cyan ink replaced with black ink, magenta ink, orange ink, purple ink, white ink, and yellow ink, respectively. At the same time, a similar trend was observed as in example 3, with essentially complete disappearance of defects at a radiation dose of 30 kGy.

Claims (27)

1. A retort package comprising a flexible multilayer substrate, said substrate comprising a reversible layer, said reversible layer comprising one or more electron beam crosslinked layers of digitally printed (meth) acrylic (co) polymer resin, containing ink formulations in which the concentration of ethylenically unsaturated groups and / or alicyclic epoxides is less than 0.2 mEq / g, and these electron-beam-crosslinked layers of ink with digital printing are characterized in that the concentration of ethylenically unsaturated groups or alicyclic epoxides is less 0.05 mEq / g, preferably less than 0.03 mEq / g, more preferably less than 0.01 mEq / g, most preferably less than 0.005 mEq / g. 2. The retort package of claim 1, wherein the reverse printed layer comprises a primer layer sandwiched between the crosslinked ink layers and the substrate. 3. Retort packaging according to claim 1 or 2, wherein the reverse-printed layer is characterized in that the total thickness of the primer layer and the ink layer (s) is from 0.4 to 4 microns, preferably from 0.6 to 3.5 microns more preferably 0.8 to 3 microns. 4. Retort packaging according to any one of paragraphs. 1-3, wherein the reverse-printed layer is characterized in that the primer thickness is 0.01 to 0.5 µm, preferably 0.05 to 0.4 µm, more preferably 0.1 to 0.3 µm. 5. Retort packaging according to any one of paragraphs. 1-4, comprising an outer structure, said outer structure containing one or more layers with a reversible print, and the lower surface of the outer structure is in contact with the upper surface of the middle structure, while the specified middle structure contains one or more barrier layers, and the lower surface middle structure is in contact with the upper surface of the inner structure, and the specified inner structure contains a sealing layer. 6. Retort packaging according to any one of paragraphs. 1-5, wherein the cross-linked ink layer of the flexible laminate remains substantially intact after autoclaving at a temperature of at least 100 ° C, preferably at least 120 ° C. 7. A method of manufacturing a flexible multilayer substrate to be used in retort packages according to any one of claims. 1-6, which includes stages at which: a) provide a flexible backing, b) applying at least one digital print with at least one ink composition by a digital printing process, said ink composition substantially free of meta (acrylic) double bonds and / or cycloaliphatic epoxy groups, c) subjecting the digital print to electron beam irradiation to form a cross-linked digital print, d) providing contact and bonding of the flexible substrate containing cross-linked digital printing on its printed side with an additional layer to form at least a portion of the multilayer substrate. 8. The method of claim 7, wherein the at least one ink composition is substantially free of components containing molecular structures with free and / or terminated ethylenically unsaturated double bonds and components containing alicyclic epoxides. 9. A method according to claim 7 or 8, wherein in step a) the flexible packaging substrate is treated with plasma, preferably corona plasma. 10. The method according to any one of claims. 7-9, including the additional step in which the primer composition is applied before starting step b). 11. The method according to any one of claims. 7-10, the digital printing process in step b) being liquid electrographic printing. 12. The method according to any one of claims. 7-11, wherein the dose of the electron beam irradiation in step c) is at least 15 kGy, preferably at least 20 kGy, more preferably at least 25 kGy. 13. The method according to any one of claims. 7-12, the dose of the electron beam irradiation in step c) being 20 to 100 kGy, preferably 25 to 80 kGy, more preferably 30 to 60 kGy. 14. The method according to any one of claims. 7-13, wherein the electron beam irradiation in step c) is carried out at an oxygen concentration of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, most preferably less than 150 ppm. 15. The method according to any one of claims. 7-14, wherein in step a) the flexible support comprises polyethylene terephthalate, high density polyethylene, oriented polypropylene, oriented polyamide or polystyrene. 16. The method according to any one of claims. 7-15, wherein the primer composition contains one or more polyacrylamides. 17. The method according to any one of claims. 7-16, wherein the ink formulation contains one or more (meth) acrylic (co) polymer resins. 18. The method according to any one of claims. 7-17, and the ink formulation contains: - from 20 to 95% by weight of the hydrocarbon liquid carrier, - from 5 to 80% by weight of one or more (meth) acrylic (co) polymer resins, - from 10 to 50% by weight of one or more carboxylated ethylenes containing copolymer co-resins and - from 0.1 to 80% by weight of one or more dyes.